The effect of corneal cap thickness on postoperative morphology in small incision lenticule extraction by finite element model.

Abstract

To investigate the impact of corneal cap thickness on postoperative deformation in small incision lenticule extraction (SMILE), we applied the finite element method (FEM). Four different strain energy density functions (the reduced polynomial model, the layered reduced polynomial model, the Holzapfel-Gasser-Ogden model, and the layered Holzapfel-Gasser-Ogden model) were considered to establish a two-dimensional axisymmetric finite element model of the cornea for simulating SMILE. The FEM was used to predict the outcomes of SMILE with a corneal lenticule with the following parameters: central thickness of 100 μm, diameter of 6.5 mm, and base thickness of 10 μm. The thickness of corneal cap (TCC) ranging from 110 μm to 160 μm in increments of 10 μm. For every model, the simulation results were obtained at an intraocular pressure of 15 mmHg. Comparisons were made between anterior and posterior corneal surface variations, corneal refractive power, and stress alterations following the removal of the corneal lenticule using various TCCs. The results showed that the posterior corneal apical displacement, corneal refractive power, and von-Mises stress at the posterior corneal apex of each model increased progressively with increasing TCC. Which means that one of the parameters that may influence postoperative corneal deformation is the thickness of the corneal cap, as it is associated with an increase in both corneal refractive power and posterior corneal apical displacement. The findings indicated that the thickness of corneal cap is an important factor affecting corneal deformation after SMILE.